In the gas and water distribution sewage and waste water industry, as well as the handling of sewage and waste waters, it is frequently necessary to join plastic pipes together and join fittings to the pipe. When thermoplastic pipe, such as polyethylene pipe, is utilized a common economical and highly effective means is to heat fuse the pipes and fittings. This is accomplished by heating the surfaces to be joined so that each reaches a molten state. While the portions of the two elements to be joined remain in a molten state, they are forced together. The molten portions intermix and adhere and, upon solidification, which occurs rapidly, the pipes or fittings are then fused together. This arrangement does not require the use of coupling devices, either threaded or otherwise, nor the use of adhesive or other chemical bonding agents.
In order to achieve a completely effective heat fusion of one thermoplastic element to another it is important that the areas to be fused together are heated to a sufficient depth so that when they are forced together a true bond occurs. The depth of bonding should be such that the welded joint has strength equal to or greater than the elements themselves.
Reference may be had to U.S. Pat. No. 3,846,208 entitled "COMBINATION PIPE FUSION UNIT", wherein apparatus and processes are described for the heat fusion of one plastic pipe to another. The apparatus and process described in the above mentioned patent includes the use of a platen having electrical heating elements and a thermostat by which the temperature of the platen may be selected. A thermometer is frequently employed for indicating to the operator when the desired temperature of the platen has been reached. If plastic pipe is to be joined end to end, that is, butt welded or butt fused, a platen which is flat on both parallel surfaces is employed. However, when a first pipe is to be joined to a second at the sidewall of the second pipe then a platen with curved surfaces must be employed, one portion being convex and the other concave to heat the portions of the pipes to be joined so that they will accurately mesh together and fuse to provide a permanent joint. The same type of platen is employed to weld a fitting to the wall of a pipe.
While platens in present use have performed satisfactorily, one problem which exists is that of heating the areas of the pipes to be fused to a sufficient depth so that the fused joint has the ultimately desired strength. Another problem with existing platens is that the flat platen surfaces provide areas wherein air may be entrapped. Entrapped air serves not only to insulate a part of the pipe so that it does not properly melt to a fusion state, but if the trapped air remains as the heated portions are forced together a void can result in the fused joint.
These and other problems exist with present platen designs and are overcome in this invention to be described.
It is, therefore, an object of this invention to provide an improved platen for use in heating portions of plastic pipe or fittings to be joined by heat fusion.
Another object of this invention is to provide an improved platen for heating portions of plastic pipe fittings to be fused together, the platen having parallel equally spaced grooves therein to increase the contact area with the portions to be fused and to thereby obtain a greater depth of melt and other advantages resulting in an improved fused joint.
These general objects as well as other and more specific objects of the invention will be fulfilled in the following description and claims, taken in conjunction with the attached drawings.